Lighting device

Abstract

One object is to provide a lighting device having a large irradiation range at low cost. One object is to provide a lighting device with improved light extraction efficiency at low cost. The lighting device includes a light-transmitting base, a first light-transmitting electrode formed over almost the whole area of a surface of the light-transmitting base, an EL layer over the first light-transmitting electrode, and a second electrode over the EL layer. The light-transmitting base has a cylindrical shape, a conical shape, a prismatic shape, or a pyramidal shape whose bottom surface is the surface of the light-transmitting base.

What is claimed is: 
     
       1. A lighting device comprising:
 a light-transmitting base; 
 a first light-transmitting electrode over a surface of the light-transmitting base; 
 an EL layer over the first light-transmitting electrode; and 
 a second electrode over the EL layer, 
 wherein the light-transmitting base has a cylindrical shape, 
 wherein a thickness of the light-transmitting base over a length of a diameter of a bottom surface of the light-transmitting base is represented by the following formula:
     h ≧(− n+ 2.34)× l,  
 
 
 wherein h is the thickness of the light-transmitting base, 
 wherein n is a refractive index of the light-transmitting base, and 
 wherein l is the length of the diameter of the bottom surface of the light-transmitting base, and 
 wherein l is 10 mm or more. 
 
     
     
       2. The lighting device according to  claim 1 , wherein the light-transmitting base includes a glass or a plastic. 
     
     
       3. The lighting device according to  claim 1 , wherein the EL layer comprises a plurality of light-emitting units which are stacked. 
     
     
       4. The lighting device according to  claim 1 , wherein the second electrode is a second light-transmitting electrode. 
     
     
       5. The lighting device according to  claim 1 , wherein the EL layer includes a transition metal oxide. 
     
     
       6. A lighting device comprising:
 a light-transmitting substrate; 
 a first light-transmitting electrode over a first surface of the light-transmitting substrate; 
 an EL layer over the first light-transmitting electrode; 
 a second electrode over the EL layer; and 
 a light-transmitting base attached to a second surface of the light-transmitting substrate which is opposite to the first surface of the light-transmitting substrate, 
 wherein the light-transmitting base has a cylindrical shape, 
 wherein a thickness of the light-transmitting base over a length of a diameter of a bottom surface of the light-transmitting base is represented by the following formula:
     h ≧(− n+ 2.34)× l,  
 
 
 wherein h is the thickness of the light-transmitting base, 
 wherein n is a refractive index of the light-transmitting base, and 
 wherein l is the length of the diameter of the bottom surface of the light-transmitting base, and 
 wherein l is 10 mm or more. 
 
     
     
       7. The lighting device according to  claim 6 , wherein the light-transmitting substrate includes a glass or a plastic. 
     
     
       8. The lighting device according to  claim 6 , wherein the EL layer comprises a plurality of light-emitting units which are stacked. 
     
     
       9. The lighting device according to  claim 6 , wherein the second electrode is a second light-transmitting electrode. 
     
     
       10. The lighting device according to  claim 6 , wherein the EL layer includes a transition metal oxide.